It is highly desirable to be able to minimize the amount of service required for internal combustion engines to thereby minimize the interruption in the use of the vehicle/equipment. Degradation of engine lubricating oil during engine use requires oil changing procedures which account for a significant portion of the maintenance and associated engine "down time". Conventional periodic oil changes generate an accumulation of waste lubricating oil which must be disposed of and/or processed resulting in undesirable costs. Therefore, extending oil drain intervals and reducing waste disposal are of great value to vehicle/equipment operators.
Consequently, systems have been developed for automatically changing internal combustion engine crankcase oil during engine operation. For example, U.S. Pat. No. 3,447,636 discloses a system for automatically changing engine oil while the engine is operating. The system operates to drain substantially all of the used oil from the engine immediately prior to introducing fresh oil into the engine from a reservoir. The single operation process results in a complete change of substantially the entire engine oil volume. However, draining the engine prior to refilling with fresh oil necessarily creates a risk that an inadequate supply of lube oil exists in the engine for an interim time period possibly resulting in damage or excessive wear to engine components from insufficient lubrication. Moreover, this system undesirably results in a quantity of waste oil.
Other systems have been developed which automatically change engine lube oil during engine operation while avoiding a waste quantity of oil by directing the used lube oil into the fuel system for burning with the fuel in the engine. These systems periodically drain a small amount of the used oil from the engine lube oil system, and replace the drained quantity with fresh lubricant from an auxiliary tank. One type of automatic oil changing system injects used lube oil into the fuel system at fixed time intervals preset by a time device. For example, U.S. Pat. Nos. 4,869,346 and 5,390,762 to Nelson disclose an automatic crankcase oil change and makeup system including a displacement unit having a piston with a predetermined stroke set to deliver identical, predetermined amounts of fresh oil during each stroke at the same flow rate and volume as the extraction of used oil. The frequency of the pressure strokes is set by a timer in an electronic controller, and is adjustably set to stroke at fixed time intervals to provide a cumulative quantity of fresh oil to the crankcase according to the regular recommended oil change period for the particular engine. A pair of dials on the controller enable the frequency of the pressure strokes to be adjusted. U.S. Pat. Nos. 4,421,078; 4,495,909; and 5,431,138 to Hurner disclose similar systems for oil changing and making up during engine operation which include a control module having an adjustable impulse timer set to periodically cycle an air pressure operated oil extractor pump at a fixed time intervals to direct a predetermined amount of engine oil out of the oil pan and into the fuel tank. Fresh makeup oil is pumped from an oil reservoir to the crankcase, also by air pressure, in response to a low level signal from a dipstick sensor. Similarly, U.S. Pat. No. 4,417,561 to Yasuhara discloses an automatic oil changing and disposing apparatus wherein used crankcase oil is periodically directed to a fuel tank via a valve controlled by an odometer switch, and fresh oil is gravity fed from a fresh oil tank to the crankcase via a control valve controlled by a crankcase oil level switch. The quantity of each increment of used oil removed from the crankcase, and each increment of fresh oil supplied, is controlled by respective timers having variable on-time duration to effect variable control of engine oil extraction and addition.
Injecting lubricating oil into engine fuel results in additional emissions related to the lube oil/fuel concentration or ratio. Upcoming government regulations may require emissions compliance at a "worst case" lube oil/fuel concentration during engine operation. Although capable of automatically changing lube oil during engine operation, the timer-based automatic oil changing systems discussed hereinabove inject more than an optimum amount of lube oil from the crankcase into the fuel system when the engine is being used less heavily than expected. As a result, these systems will likely result in an unacceptably high "worst case" lube oil/fuel concentration, especially when the engine is operated under sustained low load operation, rendering such systems extremely difficult, if not impossible, to certify due to extremely high particulate matter levels. Moreover, excessive concentrations of used oil in the fuel results in engine performance degradation, shortened fuel filter life and wasted oil. These timer-based systems also are likely to inject less than an optimum amount of lube oil into the fuel system when the engine is being used more heavily than expected. Injecting too little used oil from the oil sump into the fuel system will disadvantageously result in engine damage from over-used oil incapable of adequately lubricating and cooling engine components.
U.S. Pat. No. 5,749,339 discloses an electronically controlled continuous lubricating oil replacement system which injects the used engine lubricating oil into the engine fuel system during operation based on engine operating conditions. An electronic controller is provided to vary the amount of used lube oil injected into the fuel system based on the severity of engine operation. The system maintains the quality of the engine lube oil at a level necessary to provide optimal engine protection at all engine operating conditions. However, the "worst case" concentration may also be several times higher than the mean concentration possibly making the engine difficult to certify under strict "worst case" standards.
Japanese Patent No. 61-160509 discloses a device for mixing lube oil in a fuel tank which delivers an amount of lube oil set at a predetermined ratio relative to the incremental weight of fuel added. The oil is delivered into the fuel filling section of the fuel tank. U.S. Pat. No. 4,617,879 to Mori discloses a level sensing system that provides a signal to control a lubricant pump so as to inject an amount of oil proportional to the fuel added. However, these systems relate to two-cycle engines and therefore do not suggest removing used oil from the engine's crankcase or lubricating oil system for injection into the fuel system. Also, these systems require the oil reservoir to be replenished manually. These references also rely only on the weight and level of the fuel added.
U.K. Patent Specification No. 867,711 discloses a system for creating a controlled injection of engine lubricating oil into the engine's fuel system. The amount of oil added to the fuel system may be controlled in dependence on engine load in a first embodiment or engine speed in a second embodiment. In both embodiments, oil is injected into the fuel system via a groove formed in a fuel injection pump plunger. In the first embodiment, the annular groove is shaped with a varying cross-section. The plunger is rotated based on engine load to vary the flow area of the groove thereby varying the amount of injected oil. In the second embodiment, oil injection is controlled based on engine speed by varying the oil pressure in the suction chamber. A fuel passage containing a throttle orifice connects the fuel supply pump to the suction chamber. As the volume of fuel injected increases, the pressure in the suction chamber decreases which draws a larger quantity of oil into the chamber. However, this system delivers lubricating oil to the injection pump for injection into the engine. Moreover, this design relies on a distinct groove formed in the pump plunger to create an oil flow path. Also, since this system requires significant modifications to an engine's fuel pump, this system may not be easily retrofit on existing engines.
Therefore, there is a need for an electronically controlled engine lube oil and fuel blending system capable of simply, automatically and effectively delivering used lube oil to an engine fuel system so as to increase the oil change interval while maintaining a lube oil/fuel concentration within acceptable limits.